CN101765950B - Wavelength conversion laser device - Google Patents

Abstract

A wavelength conversion laser device (10), comprising a solid-state laser element (12) having a waveguide structure including a laser medium (121) which amplifies the laser light at a gain generated by absorption of the excitation light to output the fundamental wave, and a wavelength conversion element (13) having a waveguide structure including a nonlinear optics material (131) which converts a part of the fundamental wave output from the solid-state laser element (12) into the second harmonic wave, outputs the second harmonic wave from the wavelength conversion element (13) while oscillating the fundamental wave using a structure of an optical oscillator including the solid-state laser element (12) and the wavelength conversion element (13). The solid-state laser element (12) outputs the fundamental wave of linear polarized light, and makes the status of polarized light of the fundamental wave incoming into the solid-state laser element (12) after passing through the inside of the wavelength conversion element (13) different from that of the linear polarized light output from the solid-state laser element (12), thereby avoiding reduction of wavelength conversion efficiency of the wavelength conversion element in a peak wavelength at a gain bandwidth.

Description

Wavelength conversion apparatus

Technical field

The present invention relates to carry out by the wavelength conversion of the first-harmonic of laser medium generation, the Wavelength of Laser conversion laser aid of output predetermined wavelength.

Background technology

In recent years, as the light source in for example optical information processing field etc., researching and developing green, blue visible laser.A kind of as visible laser, known have a Wavelength conversion apparatus that uses wavelength conversion technique to make the wavelength decreases of near-infrared laser.Usually; In Wavelength conversion apparatus; At the inside of the optical resonator of semiconductor laser or solid state laser or the Wavelength conversion element that outer setting is made up of nonlinear optical material; Through being sent to Wavelength conversion element to the laser (first-harmonic) that is produced by optical resonator, output is become the second harmonic of a half-wavelength (frequency of twice) of first-harmonic by wavelength conversion.

At this moment; Must make the oscillation wavelength frequency bandwidth of optical resonator consistent with the phase matched width of Wavelength conversion element; But usually the phase matched width of Wavelength conversion element is very narrow, and the output meeting of Wavelength conversion apparatus produces fluctuation because of external environment condition.So; In order to carry out wavelength conversion expeditiously with Wavelength conversion element; Proposed in the prior art to be fixed on optical source wavelength in the allowed band of Wavelength conversion element; Not too receive the coherent source as Wavelength conversion apparatus (for example, with reference to patent documentation 1) of the formation of external environment condition variable effect.This existing coherent source; Through being transformed into high order harmonic component to first-harmonic from laser medium with Wavelength conversion element; Feed back to laser medium to the first-harmonic of the body reflection that is reflected then; Be fixed on the feedback light wavelength to the oscillation wavelength of laser medium, automatically be fixed on the oscillation wavelength of laser medium the phase matching wavelengths of Wavelength conversion element.

< patent documentation 1>TOHKEMY 2006-19603 communique

Summary of the invention

(problem that invention will solve)

In addition; In a pair of resonator mirror, have in the Wavelength conversion apparatus of inside wavelength changing type of laser medium and Wavelength conversion element; If the laser medium with having the wide gain frequency band of phase matched frequency band (wavelength conversion frequency band) than Wavelength conversion element carries out the inside wavelength conversion; Then initial first-harmonic carries out laser generation with the peak wavelength of gain frequency band, utilizes Wavelength conversion element to carry out wavelength conversion with the peak wavelength of this gain frequency band.But thus, the loss in the optical resonator of the peak wavelength of gain frequency band can increase, with the wavelength generation laser generation of the out-of-band gain frequency band of phase matched.Its result exists the first-harmonic in the phase matched frequency band to reduce, the problem that the wavelength conversion efficient of Wavelength conversion element reduces.In addition; In patent documentation 1; Though automatically be fixed on the oscillation wavelength of laser medium the phase matching wavelengths of Wavelength conversion element; But as stated, because the phase matched frequency band of Wavelength conversion element is narrower than the oscillation wavelength frequency band (gain frequency band) of laser medium generally speaking, so can not suppress the out-of-band laser generation of phase matched.

The present invention In view of the foregoing proposes just; Its purpose is to obtain in the Wavelength conversion apparatus of inside wavelength changing type; Even the peak wavelength with the gain frequency band of laser medium carries out laser generation; Carry out wavelength conversion, the Wavelength conversion apparatus that the wavelength conversion efficient of the Wavelength conversion element under the peak wavelength of gain frequency band does not also reduce.In addition, its purpose also is, need not append optics, perhaps need not append large-scale optics, just can obtain the Wavelength conversion apparatus that the wavelength conversion efficient under the peak wavelength of gain frequency band of Wavelength conversion element does not reduce.

(with the means of solve problem)

To achieve these goals, according to Wavelength conversion apparatus of the present invention, comprising: have the Solid State Laser element of the waveguiding structure that comprises laser medium, this laser medium is given the gain that produces because of the absorption exciting light, thus amplifying laser, and the output first-harmonic; And Wavelength conversion element with the waveguiding structure that comprises nonlinear optical material; This nonlinear optical material is transformed into second harmonic to the part of the first-harmonic of exporting from above-mentioned Solid State Laser element; Optical resonator structure with comprising above-mentioned Solid State Laser element and above-mentioned Wavelength conversion element makes first-harmonic resonance; And from above-mentioned Wavelength conversion element output second harmonic; This Wavelength conversion apparatus is characterised in that: the first-harmonic of above-mentioned Solid State Laser element polarization light output; And comprise filter unit, this filter unit make in above-mentioned Wavelength conversion element through and the polarization state of first-harmonic that incides above-mentioned Solid State Laser element with different from the linearly polarized light of above-mentioned Solid State Laser element output.

(effect of invention)

According to the present invention; Because need not append optics just can make the frequency band constriction; So that near the oscillation wavelength width of the first-harmonic the peak wavelength of the gain frequency band of laser medium becomes the oscillation wavelength width of first-harmonic basically; Even so utilize Wavelength conversion element to carry out wavelength conversion with the peak wavelength of laser medium, the loss in the optical resonator under this peak wavelength increases, do not produce the laser generation of the outer first-harmonic of wavelength conversion frequency band (being substantially equal to the oscillation wavelength width of first-harmonic) yet.Its result has the effect that can in the wavelength conversion frequency band of Wavelength conversion element, carry out the wavelength conversion of first-harmonic expeditiously.

Description of drawings

Fig. 1 is the stereogram of the formation of schematically illustrated execution mode 1 according to Wavelength conversion apparatus of the present invention.

Fig. 2 is the figure of electric field strength and the relation in axle orientation when the laser with the axial linearly polarized light of c being shown in nonlinear optical material, coming and going.

Fig. 3-the 1st illustrates the dependent figure that MgO:PPLN is provided with angle θ through the axial degree of polarization of the c of the laser behind the MgO:PPLN.

Fig. 3-the 2nd illustrates the dependent figure that MgO:PPLN is provided with angle θ through the axial degree of polarization of the c of the laser behind the MgO:PPLN.

Fig. 4-the 1st illustrates a direction of principal axis and the axial polarization intensity of c and the axial degree of polarization of c through the laser behind the MgO:PPLN to the dependent figure of wavelength.

Fig. 4-the 2nd illustrates a direction of principal axis and the axial polarization intensity of c and the axial degree of polarization of c through the laser behind the MgO:PPLN to the dependent figure of wavelength.

Fig. 4-the 3rd illustrates a direction of principal axis and the axial polarization intensity of c and the axial degree of polarization of c through the laser behind the MgO:PPLN to the dependent figure of wavelength.

Fig. 4-the 4th illustrates a direction of principal axis and the axial polarization intensity of c and the axial degree of polarization of c through the laser behind the MgO:PPLN to the dependent figure of wavelength.

Fig. 5-the 1st, the schematically illustrated figure that is directed against the gain shape and the relation between the laser medium gain frequency band of fundamental wavelength.

Fig. 5-the 2nd, the schematically illustrated figure that is directed against the gain shape and the relation between the laser medium gain frequency band of fundamental wavelength.

Fig. 6 is the figure of the appearance of the skew that causes of the temperature of wavelength conversion frequency band and first-harmonic in the schematically illustrated nonlinear optical material.

Fig. 7 is the stereogram of the formation of schematically illustrated execution mode 2 according to Wavelength conversion apparatus of the present invention.

Fig. 8 is the stereogram of the formation of schematically illustrated execution mode 3 according to Wavelength conversion apparatus of the present invention.

Fig. 9 illustrates through the axial polarization intensity of a of the laser behind MgO:PPLN and the quarter wave plate and the axial degree of polarization of the c dependent figure to wavelength.

(description of reference numerals)

10,10A, 10B: Wavelength conversion apparatus; 11: semiconductor laser; 12: the Solid State Laser element; 13: wavelength conversion-filter element; 13A: Wavelength conversion element; 14: half-wave plate; The 15:1/4 wave plate; 111,123a, 123b, 133a, 133b, 151: end face; 121: laser medium; 122,132: covering; 131: nonlinear optical material.

Embodiment

Below, specify preferred embodiment with reference to accompanying drawing according to Wavelength conversion apparatus of the present invention.In addition, these execution modes do not constitute restriction to the present invention.In addition, the stereogram of the Wavelength conversion apparatus that uses in the following execution mode is a sketch map, and bed thickness is different with reality with the relation of width, the ratio of each layer thickness etc.

(execution mode 1)

Fig. 1 is the stereogram of the formation of schematically illustrated execution mode 1 according to Wavelength conversion apparatus of the present invention.If this R direction shown in Figure 1 is the optical axis of the orientation of oscillation of expression laser.This Wavelength conversion apparatus 10 comprises: as the semiconductor laser 11 of exciting light source; With from the laser of semiconductor laser 11 output as exciting light, carry out as the amplification of the laser of first-harmonic and the Solid State Laser element 12 of vibration; And the wavelength conversion-filter element 13 that becomes laser beam transformation the second harmonic of 1/2 wavelength and have the function of birefringence filter from the first-harmonic of Solid State Laser element 12 output.

Semiconductor laser 11 output is used for the exciting light of pumped solid-state laser element 12.The exiting side end face 111 of the laser of this semiconductor laser 11 is arranged to the end face 123a of the laser medium 121 of Solid State Laser element 12 opposed.At this, semiconductor laser 11 is made up of the compound semiconductor materials of the laser of output wavelength 808nm.

Solid State Laser element 12 has tabular in shape, and the end face 123a vertical with optical axis R, 123b are shaped as for example rectangular shape.In addition; Solid State Laser element 12 has optical waveguide structure, absorbs the exciting light from semiconductor laser 11, forms the counter-rotating distribution; The laser that generates because of induced emission is transmitted on the direction of optical axis R, export the linearly polarized light that vibrates in predetermined direction from end face 123b.Specifically, have: absorb the flat laser medium 121 that exciting light produces induced emission; And the covering 122 that engages with one side at least in the upper and lower surface of this laser medium 121.At this; Laser medium 121 is birefringent material (being preferably the material that is made up of optics uniaxiality crystal), and its c axle (crystallographic axis) is configured to the thickness direction among the figure; One in a axle (crystallographic axis) is configured to the direction identical with optical axis R, and another is configured in the face vertical with optical axis R.It is that optic axis (optic axis) is consistent that this c axle has only one direction with the light wave speed (refractive index) in this material.

Because the orientation of oscillation of laser is the direction of optical axis R; The a axle and the c axle that in the face vertical with optical axis R, have laser medium 121 are present in by TM (horizontal magnetic) polarised light (being also referred to as unusual light) in c axle and the plane that optical axis R forms and vibration plane and are present in vertical with the plane that is formed by c axle and optical axis R and comprise TE (transverse electric) polarised light (being also referred to as normal light) in the plane of optical axis R and advance so the laser of in laser medium 121, advancing along optical axis R direction is divided into vibration plane.Under the situation of birefringent material; Laser medium 121 to TM polarized light refractive index ne and laser medium 121 to be directed against TE polarized light refractive index no different; So it is linearly polarized light that the material that has the refractive index n c that is present in scope between ne and the no through use as covering 122, can make from the laser of Solid State Laser element 12 outputs.

At this, establish Solid State Laser element 12 by constituting with the lower part: absorb from the exciting light of the 808nm of semiconductor laser 11 and export 914nm laser by Nd:YVO ₄The laser medium 121 that (refractive index during wavelength 914nm is: ne～2.17, no～1.96) constitutes; And with certain one side of the upper and lower surface of this laser medium 121 on engage by Ta ₂O ₅(refractive index during wavelength 914nm is: the covering 122 that nc～2.08) constitutes.

According to such structure; Because the TE polarised light that shows the refractive index n o littler than the refractive index n c of covering 122 that in laser medium 121, produces does not satisfy total reflection condition at the interface laser medium 121 and covering 122; So become the radial pattern that light escapes to covering 122, produce big loss.But the TM polarised light that in laser medium 121, shows the refractive index n e bigger than the refractive index of covering 122 satisfies total reflection condition at the interface laser medium 121 and covering 122, is enclosed in the laser medium 121, in fiber waveguide, transmits along optical axis R direction.Its result becomes the linearly polarized light (first-harmonic) of TM pattern from the light of Solid State Laser element 12 output.That is, from the first-harmonic of Solid State Laser element 12 outputs in thickness direction (c direction of principal axis) vibration.

Wavelength conversion-filter element 13; Has tabular; The end face 133a vertical with optical axis R, 133b are shaped as for example rectangular shape; Become the second harmonic of 1/2 wavelength from the part of the first-harmonic of Solid State Laser element 12 output by wavelength conversion, and have the function of residue first-harmonic round wavelength conversion-filter element 13 in and that incide Solid State Laser element 12 being carried out the birefringence filter of filtering.As such wavelength conversion-filter element 13; Can use MgO:PPLN (Periodically Poled Lithium Niobat; Periodic polarized lithium niobate), the nonlinear optical material of PPLT (Periodically Poled Lithium Tantalate, periodic polarized lithium tantalate) etc. with periodic polarization inversion structure.In addition; This wavelength conversion-filter element 13 also has optical waveguide structure; Can be at the upper and lower surface of nonlinear optical material 131 or wherein engage the little covering 132 of refractive index ratio nonlinear optical material 131 on certain one side, also can be the structure of air as covering.

At this, use the MgO:PPLN of hexagonal crystal systems as nonlinear optical material 131, as covering 132 on a face, use refractive index ratio PPLN to TM polarised light and the low Ta of TE polarized light refractive index ₂O ₅, and on another face, use SiO equally ₂Thus, the TM polarised light and the TE polarised light that incide in the nonlinear optical material 131 of wavelength conversion-filter element 13 satisfy total reflection condition, so transmit in wavelength conversion-filter element 13 with waveguide mode.

In addition, in order to distinguish mutually with the c axle of laser medium 121, below be expressed as the z axle to the c axle (being crystallographic axis, also is optic axis) of the nonlinear optical material (MgO:PPLN) 131 that constitutes wavelength conversion-filter element 13.And, be expressed as the x axle to a axle (crystallographic axis) of the direction parallel, being the y axle with these z axles direction indication vertical with the x axle with optical axis R.

In this execution mode 1; It is characterized in that; In order to make wavelength conversion-filter element 13 not only have the function of wavelength conversion but also to have function as the birefringence filter; Be configured to the z axle of nonlinear optical material 131 (crystallographic axis, optic axis), in the plane vertical with optical axis R with respect to the c axle tilt angle theta of laser medium 121.In addition, wavelength conversion-filter element 13, under the state of z axle with respect to the c axle inclination of laser medium 121, being cut off into its profile is tabular (rectangular-shaped).That is, the limit of the direction vertical of wavelength conversion-filter element 13 with optical axis R, parallel with the c axle with laser medium 121 with the uneven a axle of optical axis R, the y axle of the direction on these limits and nonlinear optical material 131 and the direction of z axle are inconsistent.

In above formation; On the end face 123a of semiconductor laser 11 sides of Solid State Laser element 12, form the blooming that sees through exciting light, makes the fundamental wave of laser total reflection, on the end face 123b of wavelength conversion-filter element 13 sides of Solid State Laser element 12, form the antireflection film that fundamental wave of laser is seen through.In addition; On the end face 133a of Solid State Laser element 12 sides of wavelength conversion-filter element 13, form and see through fundamental wave of laser; The blooming of reflected second harmonics laser, the blooming that on the end face 133b of the second harmonic exiting side of wavelength conversion-filter element 13, form and make the fundamental wave of laser total reflection, sees through second harmonic laser.These total reflection films and blooming constitute through range upon range of for example dielectric film.

Through as stated; The z axle of nonlinear optical material 131 that makes wavelength conversion-filter element 13 in the plane vertical with optical axis R with respect to the c axle tilt angle theta of laser medium 121; Nonlinear optical material 131 not only has as the function of wavelength conversion-filter element 13 but also has the function as the birefringence filter.

Below, be the action of this Wavelength conversion apparatus of center explanation with the function of the birefringence filter of nonlinear optical material 131.At first, from the exciting light of the end face 111 output wavelength 808nm of semiconductor laser 11, incide the end face 123a of the laser medium 121 of Solid State Laser element 12.Utilize this exciting light, in laser medium 121, form the counter-rotating distribution, get into the pattern of the photoresonance of on optical axis R direction, launching of emission naturally, this light is exaggerated because of induced emission.This light (optical resonator) between the end face 133b of the end face 123a of laser medium 121 and wavelength conversion-filter element 13 comes and goes; If but in this optical resonator, when a week, amplified gain that obtains and the loss balance that in optical resonator, when a week, causes, then laser generation would go out the laser of wavelength 914nm.

In addition, the TE polarised light in the laser that laser generation goes out as stated, owing in Solid State Laser element 12, do not satisfy total reflection condition, so lose as radial pattern, is only exported the TM polarised light from the end face of laser medium 121.That is, the laser from laser medium 121 outputs is the TM polarised light of linear polarization on the c direction of principal axis.

From the laser of laser medium 121 outputs are the axial linearly polarized lights of c, to MgO:PPLN 131 incidents.At this moment, the z axle of MgO:PPLN 131 is Nd:YVO with respect to laser medium 121 in the face vertical with optical axis R ₄C axle tilt angle theta, so linearly polarized light separates at TM polarised light that vibrates on the z direction of principal axis (unusual light) and the TE polarised light (normal light) that on the y direction of principal axis, vibrates, show different refractive indexes on one side, Yi Bian in MgO:PPLN 131, transmit.MgO:PPLN 131, owing to be wavelength conversion-filter element 13, so be transformed into the second harmonic of a half-wavelength 457nm of first-harmonic to the part of first-harmonic, export from end face 133b.In addition, the first-harmonic that is not transformed into second harmonic is returned along same path by end face 133b total reflection.

In MgO:PPLN 131, come and go, from the end face 133a of MgO:PPLN 131 through returning Nd:YVO ₄The laser of 121 first-harmonic has only the axial component of c to be selected and to Nd:YVO ₄121 incidents, the axial component of a becomes loss.For example, in MgO:PPLN131, do not have laser loss, the phase difference of the laser of vibration and transmission is 0 o'clock on z direction of principal axis and y direction of principal axis respectively, is synthesized from the light of the end face 133a ejaculation of MgO:PPLN 131, reverts to original linearly polarized light.On the other hand, produced when having produced phase difference in the process that in MgO:PPLN 131, comes and goes or when transmission when the different loss of each direction of principal axis, the light that penetrates from the end face 133a of MgO:PPLN 131 becomes circularly polarized light or elliptically polarized light.At this moment, at Nd:YVO ₄Select the polarised light (the axial polarised light of c) of first-harmonic in 121, become loss along the component of a direction of principal axis incident.

Particularly because MgO:PPLN 131 is phase plates of high order, so among MgO:PPLN 131, come and go, the phase difference of vibration and the laser that transmits is different because of wavelength on z direction of principal axis and y direction of principal axis respectively.At this moment; If the wavelength by the first-harmonic of laser medium 121 output is λ; Refringence to the laser that on z direction of principal axis and y direction of principal axis, vibrates respectively and transmit is Δ n; The crystal length of the optical axis R direction of MgO:PPLN 131 is L, and the interval delta λ that then loses minimum wavelength representes with following formula (1):

Δλ＝λ ²/2ΔnL …(1)

For example, in the MgO:PPLN 131 of crystal length L=4.0mm, if the Wavelength of Laser λ of first-harmonic=914nm, then because the Δ n=ne-no=-0.083452 of MgO:PPLN 131, so can know Δ λ=1.25nm by (1) formula.That is, minimum wavelength can periodically appear losing in every 1.25nm.

Fig. 2 is the figure of electric field strength and the relation in axle orientation when the laser with the axial linearly polarized light of c being shown in nonlinear optical material, coming and going.At this, illustrate from Nd:YVO ₄The electric field E of the laser of linear polarization on the c direction of principal axis of 121 outputs ₀, inciding MgO:PPLN 131, round trip (single through (single pass)) electric field strength when end face is exported and the relation in axle orientation.In addition, a axle and c axle are represented laser medium (Nd:YVO among the figure ₄) orientation of 121 crystallographic axis, the orientation of the axle vertical in the crystallographic axis (c axle) that z axle and y axle are represented nonlinear optical material 131 and the plane vertical with the c axle with optical axis R.

Because the intensity of the electric field of polarization on the c direction of principal axis to MgO:PPLN 131 incidents is E ₀So, if Nd:YVO ₄The angle that constitutes of the z axle of c axle and MgO:PPLN 131 (below be called angle is set) be θ, then just incided y direction of principal axis and the axial electric field component E of z behind the MgO:PPLN 131 _y, E _zUse following formula (2), (3) expression respectively:

E _y＝E ₀cosθ…(2)

E _z＝E ₀sinθ…(3)

In addition, if the intensity transmissivity that the y direction of principal axis of laser and the axial single of z pass through is respectively η _y, η _z, y direction of principal axis and the axial electric field component E of z when round trips penetrate after inciding MgO:PPLN 131 _y', E _z', according to formula (2), formula (3), use following formula (4), (5) expression respectively:

E _y’＝η _yE ₀cosθ…(4)

E _z’＝η _zE ₀sinθ…(5)

Detailed polarization characteristic about the wavelength dependency of having considered loss, refractive index; Must carry out calculating like the said use in back Jones matrix; But lose the electric field strength under the condition that becomes minimum (being that phase difference is 0) or maximum (being that phase difference is π), can irrespectively represent uniquely with the characteristic of crystal.From Nd:YVO ₄121 are transferred to MgO:PPLN 131 and incide Nd:YVO once more ₄Electric field component (E when 121 laser loses minimum (phase difference is 0) _c', E _a') and the electric field component (E during loss maximum (phase difference is π) _c', E _a'), according to formula (4), formula (5), use following formula (6), (7) expression respectively:

$\left(\begin{array}{c}{E}_c^{\&prime;}\\ E_a^{\&prime;}\end{array}\right)=\left(\begin{array}{c}{E}_0({\sqrt{{\mathrm{\&eta;}}_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HPA00001010712400012.png"\; state="\{\{state\}\}">z</figure-callout>}}}}^2{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HPA00001010712400012.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&theta;}+{\sqrt{{\mathrm{\&eta;}}_y}}^2{\sin }^2\mathrm{\&theta;})\\ ({\sqrt{{\mathrm{\&eta;}}_z}}^2-{\sqrt{{\mathrm{\&eta;}}_y}}^2)E_0\cos \mathrm{\&theta;}\sin \mathrm{\&theta;}\end{array}\right)\&CenterDot;\&CenterDot;\&CenterDot;\left(6\right)$

$\left(\begin{array}{c}{E}_c^{\&prime;}\\ E_a^{\&prime;}\end{array}\right)=\left(\begin{array}{c}{E}_0({\sqrt{{\mathrm{\&eta;}}_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HPA00001010712400012.png"\; state="\{\{state\}\}">z</figure-callout>}}}}^2{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HPA00001010712400012.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&theta;}-{\sqrt{{\mathrm{\&eta;}}_y}}^2{\sin }^2\mathrm{\&theta;})\\ ({\sqrt{{\mathrm{\&eta;}}_{\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="HPA00001010712400012.png"\; state="\{\{state\}\}">z</figure-callout>}}}}^2+{\sqrt{{\mathrm{\&eta;}}_y}}^2)E_0\cos \mathrm{\&theta;}\sin \mathrm{\&theta;}\end{array}\right)\&CenterDot;\&CenterDot;\&CenterDot;\left(7\right)$

Can find out, no matter be that the phase difference of formula (6) is 0 a situation or the phase difference of formula (7) is the situation of π, the axial intensity transmissivity η of y direction of principal axis and z _y, η _zDifference bigger and be provided with angle θ more near 45 the degree, the loss promptly along Nd:YVO ₄The component Ez ' of 121 a axle incident increases more.Fig. 3-1～Fig. 3-the 2nd is provided with the dependent figure of angle θ to MgO:PPLN through the axial degree of polarization of the c of the laser behind the MgO:PPLN.At this, the intensity transmissivity that passes through with the z direction of principal axis and the axial single of y of laser is η _z=0.9 (supposing that promptly the wavelength conversion rate that the axial single of z passes through is 10%), η _y=1.0 calculate.In addition, the axial degree of polarization of c is according to defining with respect to the axial polarization intensity of the c of c direction of principal axis and the axial polarization intensity of a sum.At this, each axial polarization intensity and this axial electric field strength square proportional.

Illustrate as these, no matter be that phase difference is that the situation that 0 situation or phase difference are π all is, the angle θ that is provided with of MgO:PPLN 131 is that the axial degree of polarization of c is minimum near 45 degree time.As shown in Fig. 3-1, the angle that is provided with of MgO:PPLN 131 is that the axial degree of polarization of 10 c when spending is 0.99964, and the angle that is provided with of MgO:PPLN 131 is that the axial degree of polarization of 45 c when spending is 0.99724.In addition, as shown in Fig. 3-2, when phase difference is π, angle θ is set is the axial degree of polarization of 45 c when spending and be roughly 0.

Below, the degree of polarization of the laser when asking laser to produce loss through time in a plurality of materials with the Jones matrix is to the dependence of wavelength.If the spin matrix of angle θ is R (θ), the phase difference of axial laser of the y of MgO:PPLN131 and the axial laser of z is α (=2 π Δ nL/ λ), and the Jones matrix J when then the z axle of MgO:PPLN 131 has tilted angle θ is represented with following formula (8):

$J=R\left(\mathrm{\&theta;}\right)\left(\begin{array}{cc}\sqrt{{\mathrm{\&eta;}}_z}& 0\\ 0& \sqrt{{\mathrm{\&eta;}}_y}\end{array}\right)\left(\begin{array}{cc}{e}^{\mathrm{i\&alpha;}/2}& 0\\ 0& e^{-\mathrm{i\&alpha;}/2}\end{array}\right)\left(\begin{array}{cc}\sqrt{{\mathrm{\&eta;}}_2}& 0\\ 0& \sqrt{{\mathrm{\&eta;}}_y}\end{array}\right)\left(\begin{array}{cc}{e}^{\mathrm{i\&alpha;}/2}& 0\\ 0& e^{-\mathrm{i\&alpha;}/2}\end{array}\right)R(-\mathrm{\&theta;})\&CenterDot;\&CenterDot;\&CenterDot;\left(8\right)$

With the Jones matrix J of this formula (8), illustrate as following formula (9), obtain the nonlinear optical material (MgO:PPLN) 131 in and incide Nd:YVO after round ₄121 o'clock electric field component (E _c', E _a').

$\left(\begin{array}{c}{E}_c^{\&prime;}\\ E_a^{\&prime;}\end{array}\right)=J\left(\begin{array}{c}{E}_z\\ E_y\end{array}\right)\&CenterDot;\&CenterDot;\&CenterDot;\left(9\right)$

Fig. 4-1～4-4 illustrates a direction of principal axis and the axial polarization intensity of c and the axial degree of polarization of c through the laser behind the MgO:PPLN to the dependent figure of wavelength.At this, the intensity transmissivity that passes through with the z direction of principal axis and the axial single of y of laser is η _z=0.9 (supposing that promptly the wavelength conversion rate that the axial single of z passes through is 10%), η _y=1.0, E _z=1, E _x=0, calculate with formula (9).Fig. 4-the 1st, the angle that is provided with of MgO:PPLN 131 is 6 figure when spending; Fig. 4-the 2nd, the angle that is provided with of MgO:PPLN 131 is 16 figure when spending; Fig. 4-the 3rd, the angle that is provided with of MgO:PPLN 131 is 26 figure when spending, Fig. 4-the 4th, the angle that is provided with of MgO:PPLN 131 is 45 figure when spending.

As shown in the c direction of principal axis degree of polarization of these figure, MgO:PPLN 131 that angle θ is set is big more, minimum wavelength and the division between the wavelength of the loss of being obtained by formula (1) is rapid more.This is because increase the then axial polarization intensity increase of a in minimum wavelength of the loss of being obtained by formula (1) and the scope between the wavelength, and this part becomes the loss when 12 incidents of Solid State Laser element if angle θ is set.

At this, angle be set be 6 degree, 16 degree, when 26 degree, 45 are spent, the axial maximum degree of polarization of c is respectively 0.9999,0.9991,0.9982,0.9972.In addition, to Nd:YVO ₄Wavelength width when the c direction of principal axis degree of polarization of the laser of 121 incidents is 90% (polarization loss is 10%) is 16 degree, 26 degree, 45 when spending in that angle is set, and is respectively 0.5nm, 0.3nm, 0.2nm.

Fig. 5-1～Fig. 5-the 2nd, the schematically illustrated figure that is directed against the gain shape and the relation between the laser medium gain frequency band of fundamental wavelength.When the first-harmonic w1 that has passed through the birefringence filter has gain shape such shown in Fig. 5-1, for example, with the wavelength location of the first-harmonic w1 of the overlap of peaks of the gain frequency band G of laser medium 121 (below be called the overlap of peaks position) λ ₁When locating laser generation, owing in wavelength conversion-filter element 13, produce second harmonic, this overlap of peaks position λ ₁The loss at place increases.At this moment, owing to λ in the overlap of peaks position ₁The region R in the outside ₁In also be that the loss that the gain of first-harmonic w1 produces greater than birefringence filter place so can carry out laser generation, produces the outer laser generation of wavelength conversion frequency band T.Because the laser that outside this wavelength conversion frequency band T, carries out laser generation is not by wavelength conversion, the wavelength conversion efficient of wavelength conversion-filter element 13 reduces.

Relative therewith, when the first-harmonic w2 that has passed through the birefringence filter has gain shape such shown in Fig. 5-2, the λ in the overlap of peaks position ₁Near outer region R ₂In, the loss that the gain of first-harmonic w2 produces less than birefringence filter place, the oscillation wavelength narrowed width of first-harmonic w2 (constriction frequency band).Therefore, though in the overlap of peaks position λ ₁Place's laser generation is because of the wavelength conversion in wavelength conversion-filter element 13 produces second harmonic, overlap of peaks position λ ₁The loss at place increases, with the λ in the overlap of peaks position ₁The gain of first-harmonic w2 near is less than the region R of laser medium gain frequency band G ₂Wavelength, laser generation can not take place.

Promptly; That hopes to obtain like this MgO:PPLN 131 is provided with angle θ; Promptly; Make the gain shape of first-harmonic w2 become, the gain frequency band G of laser medium 121 and wavelength conversion frequency band T overlapping areas and near the zone in laser generation takes place, laser generation does not take place in the wavelength beyond in this zone.More specifically, hoping becomes: near the intersection point of wavelength conversion frequency band T and laser medium gain frequency band G, and the shape of the first-harmonic w2 that the gain of first-harmonic w2 and laser medium gain frequency band G are crossing when as far as possible little among the angle θ being set angle θ being set.In addition; Since become such first-harmonic gain shape angle θ is set; Because of material, the length of wavelength conversion-filter element 13 of using are different, think the optimal angle θ that is provided with so must obtain in advance to the wavelength conversion-filter element 13 of each use.As above, can constriction to the frequency band of the laser (first-harmonic) of Solid State Laser element 12 incidents.

In addition, in Fig. 4-1～Fig. 4-4, the minimum peak position of loss is changed to 914.5nm, is that 914nm departs from from the center of wavelength conversion frequency bandwidth.This is because calculate the length of the optical axis R direction of the nonlinear optical material 131 of wavelength conversion-filter element 13 as 4.0mm.When the oscillation wavelength that makes first-harmonic was 914nm, the length that changes the optical axis R direction of nonlinear optical material 131 got final product.In addition; When the length of the optical axis R direction that constitutes nonlinear optical material 131 as stated is the Wavelength conversion apparatus 10 of 4.0mm; Change with variations in temperature owing to passed through the position of wavelength conversion frequency band of peak position, the nonlinear optical material 131 of the first-harmonic of MgO:PPLN 131, so can make both peak positions consistent through the adjustment temperature.

For example, though not shown, Wavelength conversion apparatus 10 shown in Figure 1 constitutes also and comprises: the temperature detecting unit that remains on the radiator and detect the temperature of the thermistor on radiator, installed, thermocouple etc.; Wavelength conversion apparatus 10 heating or be cooled to the heating cooling unit of amber ear card (Peltier) element, heater etc. of predetermined temperature; And control heating cooling unit is so that become the temperature control unit of predetermined temperature by the temperature of the detected radiator of temperature detecting unit (Wavelength conversion apparatus).

Fig. 6 is the figure of the appearance of the skew that causes of the temperature of wavelength conversion frequency band and first-harmonic in the schematically illustrated nonlinear optical material.At this, be 4.0mm, be example when using MgO:PPLN 131 as nonlinear optical material 131 with the length of optical axis R direction.If temperature rises, then wavelength conversion frequency band T (wavelength conversion frequency bandwidth W2) changes with+0.07nm/ ℃ ratio.On the other hand, the peak position that in MgO:PPLN 131, comes and goes the first-harmonic w3 of (from the output of birefringence filter) changes with-0.32nm/ ℃ ratio.As what calculate, because the minimum wavelength interval Δ λ of loss is 1.25nm, so whenever consistent with the peak wavelength of the gain of the first-harmonic w3 that exports from the birefringence filter at a distance from the peak of 1.25/ (0.32-0.07)=5 ℃ wavelength conversion frequency band T with formula (1).In addition, the skew of the wavelength conversion frequency band T of the MgO:PPLN 131 that causes because of 5 ℃ variations in temperature is 0.35nm (=0.07nm/ ℃ * 5 ℃), and is littler than the about 2nm of oscillation wavelength frequency bandwidth W1=of the gain frequency band G of laser medium 121.Therefore, can be through the adjustment temperature, in oscillation wavelength frequency bandwidth W1, make from the minimum peak wavelength of the loss of the first-harmonic w3 of birefringence filter output consistent with the peak of wavelength conversion frequency band T.In addition, based on by the detected temperature of temperature detecting unit, temperature control unit is controlled so that become predetermined temperature in the laser output the heat treated or the cooling processing of heating cooling unit.

According to this execution mode 1; Because the nonlinear optical material 131 as Wavelength conversion element is made up of optics uniaxiality crystal; Make its optic axis crystallographic axis angle tilt with respect to laser medium 121 in the face vertical with optical axis R to be scheduled to; So nonlinear optical material 131 is also as the birefringence filter, can restricted passage nonlinear optical material 131 incide the oscillation wavelength frequency band of the first-harmonic of Solid State Laser element 12.Its result has the effect of the wavelength conversion efficient that can improve wavelength conversion-filter element 13.In addition, also has the effect that need not increase the oscillation wavelength frequency band that components number just can limit laser.

(execution mode 2)

Fig. 7 is the stereogram of the formation of schematically illustrated execution mode 2 according to Wavelength conversion apparatus of the present invention.This Wavelength conversion apparatus 10A has such formation; Promptly; In the formation of execution mode 1, replace wavelength conversion-filter element 13 and have Wavelength conversion element 13A, this Wavelength conversion element 13A has z axle (crystallographic axis; Optic axis) is configured to the nonlinear optical material 131A that the c axle (polarization direction) with respect to Solid State Laser element 12 does not tilt, and between Solid State Laser element 12 and Wavelength conversion element 13A, inserted half-wave plate 14 as the birefringence filter.At this moment; With execution mode 1 likewise; In order to limit the wavelength band of the first-harmonic that incides Solid State Laser element 12, the optic axis p of half-wave plate 14 is got final product in the face vertical with optical axis R with predetermined angle tilt with respect to the polarization direction (the crystallographic axis c of laser medium 121) of Solid State Laser element 12.But same effect when obtaining to be obliquely installed angle θ with the following MgO:PPLN 131 of the situation of execution mode 1 gets final product half-wave plate 14 cant angle theta/2.In addition, in Fig. 7, to giving identical Reference numeral with execution mode 1 identical inscape, it explains omission.In addition, the action of the Wavelength conversion apparatus 10A in this execution mode 2 is identical with execution mode 1, so its explanation is omitted.

According to this execution mode 2, because the optic axis p of half-wave plate 14 is with respect to crystallographic axis c angle tilt to be scheduled in the face vertical with optical axis R of laser medium 121, so can limit the wavelength band of the first-harmonic of the laser that incides Solid State Laser element 12.Its result has the effect of the wavelength conversion efficient that can improve Wavelength conversion element 13A.In addition, though increased components number, the size of the optical axis direction of half-wave plate 14 is little of tens μ m, compares when appending other parts of mm level, can suppress the increase because of the size of appending the Wavelength conversion apparatus 10 that parts cause.

(execution mode 3)

Fig. 8 is the stereogram of the formation of schematically illustrated execution mode 3 according to Wavelength conversion apparatus of the present invention.This Wavelength conversion apparatus 10B has such structure,, in the formation of execution mode 1, also is provided with quarter wave plate 15 at the second harmonic outlet side of wavelength conversion-filter element 13 that is.The c axle (polarization direction) that this quarter wave plate 15 is configured to its optic axis r and Solid State Laser element 12 is same direction.But the end face 133b of the second harmonic outlet side of wavelength conversion-filter element 13 is processed into first-harmonic and second harmonic all sees through, and on the end face 151 of quarter wave plate 15, forms the first-harmonic total reflection, through the blooming of second harmonic.In addition, to giving identical Reference numeral with execution mode 1 identical inscape, it explains omission.

Fig. 9 illustrates through the axial polarization intensity of a of the laser behind MgO:PPLN and the quarter wave plate and the axial degree of polarization of the c dependent figure to wavelength.At this, with Fig. 4-1～Fig. 4-4 o'clock likewise, with the z direction of principal axis of laser and the axial single of y through in intensity transmissivity be η _z=0.9 (that is, supposing that the wavelength conversion rate that the axial single of z passes through is 10%), η _y=1.0, angle θ=16 that are provided with of MgO:PPLN 131 are spent, and calculate.In addition,, a direction of principal axis and the axial polarization intensity of c and the axial degree of polarization of c through the laser behind the MgO:PPLN 131 is shown to the dependent figure of wavelength when quarter wave plate 15 not being set, is shown in Fig. 4-2 as its comparison other.

As shown in this Fig. 9, when quarter wave plate 15 is set, with Fig. 4-2 quarter wave plate 15 is not set the time compare, to from the interval at the peak of the gain shape of the fundamental wavelength of birefringence filter (wavelength conversion-filter element 13) output at double, and the peak is by smoothing.Therefore, through quarter wave plate 15 is set, can the vibrating frequency band of first-harmonic be widened.

According to this execution mode 3; Because the z axle (optic axis) of wavelength conversion-filter element 13 tiltedly disposes in the face introversion vertical with optical axis R with respect to the c axle of laser medium 121; And the second harmonic outlet side at wavelength conversion-filter element 13 is provided with quarter wave plate 15; So have the peak smoothing that can make, the effect that the wavelength band of first-harmonic is widened from the first-harmonic of wavelength conversion-filter element 13 output.Its result can carry out wavelength conversion expeditiously.In addition, in Fig. 7 of execution mode 2, at the second harmonic outlet side of Wavelength conversion element 13A quarter wave plate is set likewise and also can obtains same effect.

In addition; In execution mode 2,3, with execution mode 1 likewise, also can through control Wavelength conversion apparatus temperature; In the oscillation wavelength frequency bandwidth, make by the minimum peak wavelength of the loss of the first-harmonic of birefringence filter output consistent with the peak of wavelength conversion frequency band.

And; In above-mentioned explanation; Situation about being located at the optic axis (c axle) of the laser medium 121 of Solid State Laser element 12 on the thickness direction of flat laser medium 121 is that example is illustrated; But as long as a axle and optical axis R dispose abreast, the optic axis of laser medium 121 (c axle) is present in the face vertical with optical axis R, and the optic axis of laser medium 121 (c axle) is provided with on which direction can.In addition; At this moment also be; Resemble and make the optic axis (c axle) of the nonlinear optical material 131 of wavelength conversion-filter element 13 or Wavelength conversion element 13A or the optic axis p of half-wave plate above-mentioned, get final product with predetermined angle tilt configuration with respect to the optic axis (c axle) of laser medium 121.

Utilizability in the generation

As stated, when being transformed into second harmonic to the laser of predetermined wavelength expeditiously, Wavelength conversion apparatus according to the present invention is useful.

Claims (6)

1. Wavelength conversion apparatus comprises:

The Solid State Laser element has the waveguiding structure that comprises laser medium, and give the gain that produces because of the absorption exciting light and come amplifying laser, and the output first-harmonic;

Wavelength conversion element; Be transformed into second harmonic to the part of the first-harmonic of exporting from above-mentioned Solid State Laser element; Make in above-mentioned Wavelength conversion element through and the polarization state of first-harmonic that incides above-mentioned Solid State Laser element with different from the linearly polarized light of above-mentioned Solid State Laser element output; This Wavelength conversion element has the waveguiding structure that comprises nonlinear birefringent optical material; The optic axis of this birefringent optical material optic axis with respect to above-mentioned laser medium in the face vertical with the optical axis of above-mentioned laser disposes with predetermined angle tilt; Should predetermined angle be selected as: in the overlapped zone of the gain frequency band of above-mentioned laser medium and wavelength conversion frequency band, make the gain shape generation laser generation of the first-harmonic that has passed through above-mentioned birefringent optical material; And

The optical resonator structure makes first-harmonic resonance, and from above-mentioned Wavelength conversion element output second harmonic, comprises above-mentioned Solid State Laser element and above-mentioned Wavelength conversion element.

2. Wavelength conversion apparatus as claimed in claim 1 is characterized in that:

Second harmonic outlet side at above-mentioned Wavelength conversion element also comprises quarter wave plate, and the optic axis of this quarter wave plate is configured on the direction identical with the optic axis of above-mentioned laser medium.

3. Wavelength conversion apparatus as claimed in claim 1 is characterized in that:

Above-mentioned predetermined angle is selected as: laser generation takes place in the gain shape that makes the above-mentioned first-harmonic that has passed through above-mentioned birefringent optical material in overlapped zone of the gain frequency band of above-mentioned laser medium and above-mentioned wavelength conversion frequency band and near the zone it, and laser generation does not take place the wavelength beyond in this zone.

4. Wavelength conversion apparatus as claimed in claim 1 is characterized in that:

Above-mentioned predetermined angle is: near the intersection point of the gain frequency band of above-mentioned wavelength conversion frequency band and above-mentioned laser medium, the gain frequency band of the gain shape of above-mentioned first-harmonic and above-mentioned laser medium intersects is provided with the angle with smallest in the angle.

5. Wavelength conversion apparatus comprises:

The Solid State Laser element has the waveguiding structure that comprises laser medium, and give the gain that produces because of the absorption exciting light and come amplifying laser, and the output first-harmonic;

Wavelength conversion element is transformed into second harmonic to the part of the first-harmonic of exporting from above-mentioned Solid State Laser element, has the waveguiding structure that comprises nonlinear birefringent optical material;

The optical resonator structure makes first-harmonic resonance, and from above-mentioned Wavelength conversion element output second harmonic, comprises above-mentioned Solid State Laser element and above-mentioned Wavelength conversion element; And

Half-wave plate; Between above-mentioned Solid State Laser element and above-mentioned Wavelength conversion element, dispose; The optic axis of this half-wave plate optic axis with respect to above-mentioned laser medium in the face vertical with the optical axis of above-mentioned laser disposes with predetermined angle tilt; Make in above-mentioned Wavelength conversion element through and the polarization state of first-harmonic that incides above-mentioned Solid State Laser element with different from the linearly polarized light of above-mentioned Solid State Laser element output

The above-mentioned nonlinear birefringent optical material of above-mentioned Wavelength conversion element is made up of following birefringent material, and the optic axis of this birefringent material is configured on the direction identical with the optic axis of above-mentioned laser medium.

6. Wavelength conversion apparatus as claimed in claim 5 is characterized in that:

Second harmonic outlet side at above-mentioned Wavelength conversion element also comprises quarter wave plate, and the optic axis of this quarter wave plate is configured on the direction identical with the optic axis of above-mentioned laser medium.

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